Biomolecules are the building blocks of life. They are chemical compounds that are present in living organisms and perform essential biological functions. Understanding biomolecules is crucial for Class 12 students because this topic is frequently asked in CBSE board exams, NEET, and other competitive exams. Biomolecules include carbohydrates, proteins, lipids, nucleic acids, and enzymes.
These molecules are responsible for energy storage, structural support, catalysis of reactions, and genetic information transfer. This detailed note will help you understand, memorize, and revise all important aspects of biomolecules.
Biology Class 12 Biomolecules Notes – Detailed NCERT Notes & Important Questions
1. Carbohydrates
Definition:
Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen in the ratio C:H:O = 1:2:1. They are also called saccharides.
Classification:
- Monosaccharides: Simple sugars that cannot be hydrolyzed further.
- Examples: Glucose, Fructose, Galactose
- Properties: Sweet, soluble in water, reducing sugars.
- Function: Immediate source of energy.
- Disaccharides: Formed by two monosaccharides via glycosidic bond.
- Examples: Sucrose (Glucose + Fructose), Lactose (Glucose + Galactose), Maltose (Glucose + Glucose)
- Function: Transport form of sugar in plants (Sucrose) and milk sugar (Lactose).
- Polysaccharides: Long chains of monosaccharides.
- Examples: Starch, Glycogen, Cellulose, Chitin
- Function: Energy storage (Starch in plants, Glycogen in animals), Structural support (Cellulose in plants, Chitin in arthropods).
Important Note:
- Monosaccharides: Reducing sugars
- Disaccharides: Sucrose is non-reducing
- Polysaccharides: Non-reducing
2. Proteins
Definition:
Proteins are polymers of amino acids joined by peptide bonds. They contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
Amino Acids:
- Building blocks of proteins.
- Each amino acid has an amino group (-NH2), carboxyl group (-COOH), hydrogen atom, and R group (side chain) attached to a central carbon.
Protein Structure:
- Primary Structure: Linear sequence of amino acids.
- Secondary Structure: Folding of chain into α-helix or β-pleated sheet due to hydrogen bonding.
- Tertiary Structure: 3D folding of a single polypeptide chain.
- Quaternary Structure: Association of two or more polypeptide chains (e.g., Hemoglobin).
Functions of Proteins:
- Structural: Collagen, Keratin
- Transport: Hemoglobin, Myoglobin
- Enzymatic: Catalysts in biochemical reactions
- Defensive: Antibodies
- Regulatory: Hormones like Insulin
- Storage: Casein (milk), Ferritin (iron storage)
3. Lipids
Definition:
Lipids are hydrophobic biomolecules composed of carbon, hydrogen, and oxygen, and sometimes phosphorus.
Classification:
- Simple Lipids (Fats and Oils): Composed of glycerol + fatty acids (Triglycerides).
- Compound Lipids: Contain additional groups like phosphate (Phospholipids).
- Derived Lipids: Derived from simple and compound lipids (e.g., Steroids like Cholesterol).
Functions:
- Long-term energy storage
- Insulation and protection of organs
- Structural component of membranes (Phospholipids)
- Hormone synthesis (Steroids)
4. Nucleic Acids
Definition:
Nucleic acids are polymers of nucleotides and are responsible for storing and transmitting genetic information.
Types:
- DNA (Deoxyribonucleic acid): Double-stranded, stores genetic info, contains deoxyribose sugar.
- RNA (Ribonucleic acid): Single-stranded, involved in protein synthesis, contains ribose sugar.
Nucleotide Structure:
- Phosphate group
- Pentose sugar (Ribose or Deoxyribose)
- Nitrogenous base (Adenine, Thymine, Guanine, Cytosine, Uracil in RNA)
Functions:
- DNA: Genetic material in cells
- RNA: Protein synthesis (mRNA, tRNA, rRNA)
5. Enzymes
Definition:
Enzymes are biological catalysts that speed up chemical reactions without being consumed.
Properties:
- Highly specific to substrates
- Work under mild conditions (pH, temperature)
- Can be denatured by extreme conditions
Examples:
- Amylase: Breaks starch into sugar
- Lipase: Breaks fats into glycerol and fatty acids
- Protease: Breaks proteins into amino acids
6. Vitamins (Biomolecules with Special Functions)
- Water-soluble: B-complex, C
- Fat-soluble: A, D, E, K
- Function: Act as coenzymes or regulators in metabolic reactions.
Important Questions for Exams
- Define biomolecules and classify them with examples.
- Difference between monosaccharide, disaccharide, and polysaccharide.
- Structure and function of DNA and RNA.
- Explain primary, secondary, tertiary, and quaternary structures of proteins.
- Functions of lipids in living organisms.
- Role of enzymes in biochemical reactions.
- What are vitamins and their importance?
Conclusion
Biomolecules are the fundamental components of life, each with a unique structure and function. A strong understanding of carbohydrates, proteins, lipids, nucleic acids, and enzymes is essential not only for Class 12 exams but also for competitive exams like NEET and JEE. Revising these notes, remembering key functions, and practicing diagrams will ensure excellent exam preparation.
Class 12 Biomolecules – Important & Repeated Questions
1. Carbohydrates
- Define carbohydrates and classify them with examples. (Repeated in CBSE 2021, 2022)
- Write the difference between monosaccharides, disaccharides, and polysaccharides. (Repeated in NEET 2020)
- Explain the structure and function of starch and cellulose. (Repeated in CBSE 2020, 2023)
- Give examples of reducing and non-reducing sugars.
- Draw the structure of glucose (both α and β forms). (Repeated in CBSE 2022)
2. Proteins
- Define proteins and write their functions. (CBSE 2021, NEET 2020)
- Describe the primary, secondary, tertiary, and quaternary structure of proteins. (Repeated in multiple exams)
- Explain the structure and function of hemoglobin.
- Difference between globular and fibrous proteins. (CBSE 2022)
- Explain peptide bond formation with a diagram.
3. Lipids
- Define lipids and classify them with examples. (Repeated in CBSE 2019, 2021)
- Explain the structure and function of triglycerides.
- What are phospholipids? Describe their role in cell membranes. (CBSE 2020, NEET 2021)
- Difference between saturated and unsaturated fatty acids.
- Explain the biological importance of lipids.
4. Nucleic Acids
- What are nucleic acids? Classify them. (Repeated in CBSE 2020, 2022)
- Describe the structure of DNA and RNA with labeled diagrams. (NEET 2019, 2021)
- Explain the difference between DNA and RNA.
- Explain the role of nucleotides in energy transfer.
- What is the function of mRNA, tRNA, and rRNA in protein synthesis? (Repeated in multiple exams)
5. Enzymes
- Define enzymes and explain their characteristics. (Repeated in CBSE 2021)
- Differentiate between enzymes and chemical catalysts.
- Explain enzyme specificity with examples.
- What is the effect of temperature and pH on enzyme activity? (CBSE 2020, NEET 2020)
- Describe the mechanism of enzyme action (Lock & Key and Induced Fit Model).
6. Vitamins
- Define vitamins and classify them. (Repeated in CBSE 2019, 2021)
- Mention the sources, deficiency symptoms, and functions of fat-soluble vitamins (A, D, E, K). (NEET 2020, 2022)
- Mention the sources, deficiency symptoms, and functions of water-soluble vitamins (B-complex, C).
- Role of vitamins as coenzymes in metabolism.
Extra Tips for Exams
- Always remember monosaccharides, disaccharides, and polysaccharides examples.
- Diagrams of DNA, RNA, peptide bond, hemoglobin, and glucose are often asked.
- Vitamins table (sources + deficiency) is a frequent question.
- Repeated conceptual questions usually come from: functions, differences, classification, and structure.
We are Completed Biology Class 12 Biomolecules Notes